import java.util.Scanner;

public class Fib {
    public static void main(String[] args) {
        int n;
        Scanner scanner = new Scanner(System.in);
        n = scanner.nextInt();
        System.out.println( new  Test().fun( n ));
    }
}

 class  Test {

    long fun(int n) {
        if (n == 1 || n == 2) {
            return 1;
        }
        return fun(n - 1) + fun(n - 2);
    }
}